Forest type preference of an Afrotropical thrush (East Coast Akalat

Forest type preference of an Afrotropical thrush (East Coast Akalat, Sheppardia gunningi sokokensis)
in Arabuko‐Sokoke Forest, Kenya
J.E. Banks*††, C. Jackson†¥, Albert Baya †, H. Minnella*, M. Nitz*, J. Hitchcock*, D. Bruinsma‡
* Environmental Science, Interdisciplinary Arts & Sciences, University of Washington, Tacoma, WA 98402‐3100. † A Rocha Kenya, PO Box 383, Watamu, Kenya ¥ Ornithology Section, National Museums of Kenya, PO Box 40658, Nairobi, Kenya
‡ University of Manitoba, Winnipeg, Canada Concern
• Loss of habitat through land conversion and resource extraction
– (Brooks and Thompson 2001, Birdlife International 2005) • One in every eight bird species is expected to be extinct within a hundred years given current population trends – (Birdlife International 2005)
Benefits of Avian Populations
• Avian populations provide ecosystem services including
– Pest control
– Pollination
– Seed dispersal
– Maintenance of food webs Mida Creek look out
• Enhance economic gain due to bird tourism
Habitat and Avian Conservation
• Vegetation
– Species abundance is highly dependent on individual habitat preferences and the availability of the preferred habitat type (Van Rensburg et al. 2000)
• Disturbances
– Bird populations are found to still decline steadily in regions that were not protected against human impact and settlement (Buchanan et al 2009)
– The larger the forest fragment and further from human disturbance the greater the abundance and diversity of birds (Aubad et al 2010)
Important Bird Areas (IBAs)
• Birdlife International
• Prioritize areas of conservation need • The African continent
– Over 300 bird species of concern
– There are 1,230 IBAs in 58 territories (Githiru 2008)
www.birdlife.org/regional/africa/pdfs/ribacs_africa.pdf
Arabuko‐Sokoke Forest (ASF)
• Outside of Watamu, Kenya
• Encompasses the largest remnant patch of indigenous coastal forest in East Africa
• Over 400km2 in area Arabuko‐Sokoke Forest Contains three distinct habitat types:
– Brachystegia woodland • named for the dominant species Brachystegia
spiciformis Bentham
– Cynometra forest and thicket • named for the dominant species Cynometra
webberi Baker f.
– Mixed forest
• characterized by a densely‐
packed diverse mixture of tree and shrub species
(Nemeth and Bennun 2000)
Arabuko‐Sokoke Forest
Several endangered and rare species
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Sokoke Bushy‐tailed Mongoose
– Bdeogale omnivora Heller
Aders’ Duiker
– Cephalophus adersi Thomas
Golden‐rumped Elephant Shrew
– Rhynchocyon chrysopygus Günther.
African elephants
– Loxodonta africana Blumenbach
– approx. 150
Arabuko‐Sokoke Forest Home to six birds of concern
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Spotted Ground Thrush
– Zoothera guttata Vigors
Sokoke Pipit
– Anthus sokokensis van Someren
Sokoke Scops Owl
– Otus ireneae Ripley
Amani Sunbird
– Anthreptes pallidigaster Sclater & Moreau
Clarke’s Weaver
– Ploceus golandi Clarke East Coast Akalat
– Sheppardia gunningi sokokensis
Haagner (Bennun & Njoroge, 1999) ECA Behavior
Feeding primarily on insects (with supplemental berries and seeds)
• Thrives in open forest understory with some vegetative cover a few meters above the ground and ample leaf litter, which is linked to higher beetle populations
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– (Matiku et al. 2000, Nemeth and Bennun 2000, Banks et al. 2010).
Relies on ground cover and organic matter for nesting materials
• conservation efforts have focused on forestry practices, with particular emphasis on reduced logging and forest clearing.
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East Coast Akalat (ECA) Status
• Serves as an indicator species
• Formerly ranging from Kenya down to Malawi and Mozambique along the east African coast • Now most abundant in the coastal forests of Kenya
• Largest remnant population (approx. 7500 pairs) residing year‐round in the ASF reserve
– (Birdlife International, 2008)
• Classified as Near Threatened (likely to be threatened in the near future) by the World Conservation Union’s
– (www.iucnredlist.org)
Methods: Point Counts by means of Playback
200 m
2 km
• Conducted in the years 2005, 2007, 2008 and 2010
• Conducted during the breeding season spanning November, December, and early January between 6:00‐9:00 am
– the species tends to call most vigorously during this time.
• A portable speaker system was used to play S. gunningi calls recorded by the observers in the same forest
Discussion
• A principal difference between Cynometra and Mixed forest is the soil composition.
– Cynometra,
• Western part of the reserve
• Dominated by one tree species
• Dry, red Magarini soils. – Mixed forest • Eastern part of the reserve
• Diverse vegetation
• Wetter, grey, sandy soil (Nemeth and Bennun 1999). Foot print of African Elephant in ASF
Discussion: African Elephant (Loxodonta africana) Disturbance
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Known to alter habitat structure • Reducing tree heights and increasing brush (Cumming and Fenton 1997, Guidemond and Van Aarde 2008)
• Facilitating dispersal and germination of seeds (Brachmarchary 1980, Muoria et al. 2001)
• Modifying soil condition and nutrients (Hatton and Smart 1984).
Alter habitat critical to the survival of arthropods important to their diets
– (Van Rooyen et al. 1994, Skarpe et al. 2004, Banks et al. 2010). Mixed forest habitat contains significant water resources for the L. africana
population thus is subject to severe vegetation and habitat alteration in many places (JEB pers. obs.).
Damage Caused by Elephants in ASF
Discussion: Human Disturbance
• Identified as a major threat to the conservation of biological diversity in ASF
– (Arabuko‐Sokoke Forest Management Team 2002).
• The use of forest products for fuelwood, poles, food, and medicinal plants by residents of the 50+ villages surrounding the reserve continues to threaten the charcoal off of Mombasa road from
persistence of S. gunningi Selling
Nairobi (Photo courtesy of John Banks)
and other species of concern.
Future Research Needs
• A more thorough assessment of the full extent of vegetation heterogeneity within each of the three habitat zones in ASF would enhance our understanding of the precise relationship between akalat densities and habitat heterogeneity. • Further exploration of elephant behavior in the Mixed forest influencing akalat habitat preference indirectly via effects on arthropod resources and vegetation structure
• Better quantitative estimates of forest extraction coupled with ongoing environmental education programs (e.g., ASSETS) and the development of alternative sources of income for locals can help enhance stewardship and sustainability of the reserve. Citations
Arabuko‐Sokoke Forest Management Team (2002) Arabuko‐Sokoke strategic forest management plan 2002‐2027. BirdLife International.
Aubad J, Aragon P, Rodriguez MA. 2010. Human access and landscape structure effects on Andean forest bird richness. Acta Oecologica. 36: 396‐
402.
Banks JE, Jackson C, Hannon LM, Thomas CM, Baya A, Njoruge L. 2010. The cascading effects of elephant presence/absence on arthropods and an Afrotropical thrush in Arabuko‐Sokoke Forest, Kenya. African Journal of Ecology 48(4): 1030‐1038.
Bennun L, Njoroge P. 1999. Important bird areas in Kenya. Nairobi: East Africa Natural History Society.
Birdlife International. 2005. Globally threatened birds: indicating priorities for action. Birdlife International, Cambridge, United Kingdom. http://www.birdlife.org/action/science/species/globally_tbu/gtb_booklet.pdf
Birdlife International. 2008. East Coast Akalat. BirdLife Species Fact Sheet. www.birdlife.org.
Brachmachary RL. 1980. On the germination of seeds in the dung balls of the African elephant in the Virunga National Park. Terre et Vie 34: 139‐
142.
Brooks T, Thompson H S 2001. Current Bird Issues in Africa. The Auk. 118 (3): 575‐582.
Brooks T, Balmford A, Burgess N, Hansen LA, Moore J, Rahbeck C et al. 2001. Conservation priorities for birds and biodiversity: Do East African Important Bird Areas represent species diversity in other terrestrial vertebrate groups? Ostrich. 72:Suppl 15, 3‐12.
Buchanan GM, Donald PF, Fishpool LDC, Arinaitwe JA, Balman M, Mayaux P. 2009 An assessment of land cover and threats in Important Bird Areas in Africa. Bird Conservation Internaional. 19: 49‐61. Cumming DHM, Fenton MB. 1997. Elephants, woodlands, and biodiversity in southern Africa. South African Journal of Science. 93: 231‐236. Githiru M. 2008. Conservation of birds in Africa: are we making any headway? African Journal of Ecology 46: 233‐234.
Guidemond R, Van Aarde R. 2008. A meta‐analysis of the impact of African elephants on savanna vegetation. Journal of Wildlife Management 72: 892‐899.
Hatton JC, Smart NOE. 1984. The effect of long‐term exclusion of large herbivores on soil nutrient status in Murchison Falls National Park, Uganda. African Journal of Ecology 22: 23‐30.
Muoria PK, Gordon I, Oguge NO. 2001. Elephants as seed dispersal agents in Arabuko‐Sokoke Forest, Kenya. Pachyderm 30: 75‐80. Nemeth E, Bennun L. 2000. Distribution, habitat selection and behavirous of the East Coast Akalat Sheppardia gunningi sokokensis in Kenya and Tanzania. Bird Conservation International 10: 115‐130.
Ogada DL, Gadd ME, Ostfeld RS, Young TP, Keesing F. 2008. Impacts of large herbivorous mammals on bird diversity and abundance in an African savanna. Oecologia 156: 387‐397. Van Rensburg BJ, Chown SL, Van Jaarsweld AS, McGeoch MA. 2000. Spatial variation and biogeography of forest avian assemblages in South Africa. Journal of Biogeography 27: 385‐401. Acknowledgments
John “Buck” Banks
Collin Jackson Mwamba Field Station crew
Maria Nitz and Jason Hitchcock
University of Washington Royalty Research Fund Grant
• University of Washington Tacoma Founders' Endowment Award
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Questions?